Tonometers are well-known devices for detecting the intraocular pressure within an eye. There are several types of tonometers available. In general, the commercially available tonometers require that the eyelid be open, and a contact directly or indirectly is made with the open eye. For example, one type of tonometer uses a jet of gas that impinges against the open eye. Another type has a probe that makes physical contact with the open eye. Such conventionally tonometers are expensive, and not particularly accurate. Moreover, their use frequently irritates the patient's eye. Consequently, it would be desirable to provide a tonometer that could detect the intraocular pressure through the closed eyelid of a patient. In U.S. Pat. No. 7,288,067 such a tonometer is disclosed.